Re: Remote Turn-On



Mike DeAngelis wrote: 
Hi,
    Does anyone have a schematic, kit, or a complete product to sense a line
level audio signal and turn a remote power amplifier on? I have done all the
searches I can think of and have not found anything. These things can't be
that rare!!
    Thanks...Mike DeAngelis



The audio line activated switch is not VOX as some have claimed- VOX is largely a radio term and describes detecting a few tens of mV or less of microphone output. Your circuit is working off of 100mV,RMS minimum, and up to 2V,RMS, into 10K loading. All you need to do is gain that up, rectify, smooth, and drive a relay. Actually, you don't need to do any of that using a single transistor and a CMOS 555. The circuit below uses a 2N3904 to gain up the line input to a 5Vpp swing at the 555 TRIG input. As long as the 555 receives triggers before the 15u can discharge, which takes about 2 mins, it will remain on keeping the relay activated. No adjustment should be necessary.
View in a fixed-width font such as Courier.

..
..
..
..                                              NEUT ------------->
..                                              GND  -+----------->
..                                                    |
..                                        .-----------'
..                                        |
..                            (-)---------+     HOT  -----o---v
..                        5V              |                   o--->
..                            (+)---------|---------.
..                                        |100u +   |       |
..                                        +--||-----+
..                                    \   |         |       |
..                                    \|--+--||-----+
..                                    \|   0.1U     |       |
..                                                  |    --------
..                      .-----+----+------+---------+---|/ / / / |-.
..  AUDIO               |     |    |      |         |    --------  |
..  LINE 0.022u         |     |   +|      |         +------|<|-----+
..  IN>--+-||--.        |     |   ===   [120K]      |     1N4001   |
..       |     |     [100K] [10M] 15U     |         |              |
..       |     |        |     |    |      |   TLC555------.        |
..       |   [10K]      |     |    |      |   |  VCC/RST  | 2N4401 |
..       |     |        |     |    |      |   |           |      |/
..       |     +-[4.7M]-+-|<|-+----+----------|THRESH  OUT|-[1K]-|
..       |     |        |1N4148    |      |   |           |      |>
..       |     |   22p  |          |      |   |           |        |
..       |     +---||---+-----------------|---|TRIG    DIS|--.     |
..       |     |        |          |      |   |           |  |     |
..       |     |        |          |      |   |           |  |     |
..       |     |      |/           |      +---|CONT       |  |     |
..       |     '------|2N3904      |      |   |           |  |     |
..       |            |>           |      |   |      GND  |  |     |
..       |              |          |      |   '-----------'  |     |
..     [1M]             |          |      |           |      |     |
..       |              |          |    [100K]        |      |     |
..       |              |          |      |           |      |     |
..       |              |          |      |           |      |     |
..       |              |          |      |           |      |     |
..       '--------------+-----------------+-----------+------|-----'
..                      |          |                         |
..                     ---         |                         |
..                     ///         '-------------------------'
..

.

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